Organic electroluminescent materials and devices

ABSTRACT

Novel phosphorescent tetradentate platinum compounds of Formula I are provided. The complexes contain a dibenzo moiety, which allows for the creation of OLED devices with improved properties when compounds of Formula I are incorporated into such devices. Compounds of Formula I′ that comprise two ligands that contain a 5-membered carbocyclic or heterocyclic ring, one of which contains an imidazole ring with a twisted aryl group attached to N−1 and a second aromatic ring that is attached to the platinum via a carbon atom. These compounds may be advantageously used in OLEDs.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. Application Ser. No. 61/541,769, filed Sep. 30, 2011 and to European Application No, 12177646.2 filed Jul. 24, 2012 which claims priority to U.S. Application Ser. No. 61/511,385, filed Jul. 25, 2011, the disclosures of which are herein expressly incorporated by reference in their entirety.

The claimed invention was made by, on behalf of, and/or in connection with one or more of the following parties to a joint university corporation research agreement: Regents of the University of Michigan, Princeton University, The University of Southern California, and the Universal Display Corporation. The agreement was in effect on and before the date the claimed invention was made, and the claimed invention was made as a result of activities undertaken within the scope of the agreement.

FIELD OF THE INVENTION

The present invention relates to compounds suitable for incorporation into OLED devices, specifically the compounds comprise tetradentate platinum complexes. The compounds also comprise cyclometallated tetradentate Pt(II) complexes comprising two ligands that each contain at least one 5-membered carbocyclic or heterocyclic ring. One ligand comprises an imidazole ring with a twisted aryl group bonded to N−1 and an aromatic ring that is coordinated to the platinum via, a carbon atom.

BACKGROUND

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.

As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.

As used herein, “solution processable” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.

More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

A compound having the formula:

is provided, wherein G has the structure

and wherein G is fused to any two adjacent carbon atoms on ring A. Ring B, ring C, and ring D are 5- or 6-membered carbocyclic or heterocyclic aromatic rings. L₁, L₂, and L₃ are independently selected from the group consisting of a single bond, BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. At least one of L₁, L₂, and L₃ is not a single bond, and X is selected from the group consisting of BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. Z₁, Z₂, Z₃, and Z₄ are nitrogen or carbon atoms, and A₁, A₂, A₃, A₄, A₅, A₆, A₇, and A₈ comprise carbon or nitrogen. R₁, R₂, R₃, and R₄ independently represent mono-, di-, tri-, or tetra-substitution, wherein R₁ is optionally fused, R₂ is optionally fused to ring B, R₃ is optionally fused to ring C, and R₄ is optionally fused to ring D. R₃ and R₁ are optionally linked to form a ring. If L₂ is not a single bond, R₃ and L₂ or R₄ and L₂ are optionally linked to form a ring. R, R′, R₁, R₂, R₃, and R₄ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one embodiment, the compound has a neutral charge. In one embodiment, at least two of Z₁, Z₂, Z₃, and Z₄ are nitrogen atoms. In another embodiment, at least two of Z₁, Z₂, Z₃, and Z₄ are carbon atoms.

In one embodiment, at least one of ring B, ring C, and ring D comprises a carbene ligand coordinated to Pt. In another embodiment, at least one of Z₁, A₁, A₂, A₃, A₄, A₅, A₆, A₇, and A₈ is a nitrogen atom.

In one embodiment, the compound has the formula:

In another embodiment, the compound has the formula:

In one embodiment, the compound has the formula:

wherein Y is selected from the group consisting of BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′.

In another embodiment, the compound has the formula:

In one embodiment, L₁ and L₂ are single bonds. In another embodiment, L₃ is independently selected from the group consisting of O, S, and NR. In another embodiment, L₃ is NR, and R is phenyl or substituted phenyl. In one embodiment, L₃ is O.

In one embodiment, Z₂ and Z₃ are nitrogen atoms. In another embodiment, Z₂ and Z₄ are nitrogen atoms. In one embodiment, X is independently selected from the group consisting of O, S, and NR. In one embodiment, X is O.

In one embodiment, the compound is selected from the group consisting of:

wherein Y is selected from the group consisting of BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. A₁′, A₂′, A₃′, A₄′, A₅′, A₆′, A₇′, and A₈′ comprise carbon or nitrogen. At most one of A₁, A₂, A₃, A₄ is nitrogen, and at most one of A₁′, A₂′, A₃′, A₄′ is nitrogen. At most one of A₅, A₆, A₇, A₈ is nitrogen, and the nitrogen is not bound to Pt. At most one of A₅′, A₆′, A₇′, A₈′ is nitrogen, and the nitrogen is not bound to Pt. The Pt forms at least two Pt—C bonds and R₃ and R₄ may be fused together to form a ring. R₅ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

A first device is provided. The first device comprises a first organic light emitting device, further comprising an anode, a cathode, and an organic layer, disposed between the anode and the cathode, comprising a compound having the formula:

is provided, wherein G has the structure

and wherein G is fused to any two adjacent carbon atoms on ring A. Ring B, ring C, and ring D are 5- or 6-membered carbocyclic or heterocyclic aromatic rings. L₁, L₂, and L₃ are independently selected from the group consisting of a single bond, BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. At least one of L₁, L₂, and L₃ is not a single bond, and X is selected from the group consisting of BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. Z₁, Z₂, Z₃, and Z₄ are nitrogen or carbon atoms, and A₁, A₂, A₃, A₄, A₅, A₆, A₇, and A₈ comprise carbon or nitrogen, R₁, R₂, R₃, and R₄ independently represent mono-, di-, tri-, or tetra-substitution, wherein R₁ is optionally fused, R₂ is optionally fused to ring B, R₃ is optionally fused to ring C, and R₄ is optionally fused to ring D. R, R′, R₁, R₂, R₃, and R₄ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one embodiment, the first device is a consumer product. In another embodiment, the first device is an organic light-emitting device, in one embodiment, the first device comprises a lighting panel. In one embodiment, the organic layer is an emissive layer and the compound is an emissive dopant. In another embodiment, the organic layer is an emissive layer and the compound is a non-emissive dopant.

In one embodiment, the organic layer further comprises a host. In another embodiment, the host comprises a triphenylene containing benzo-fused thiophene or benzo-fused furan, wherein any substituent in the host is an unfused substituent independently selected from the group consisting of C_(n)H_(2n+1), OC_(n)H_(2n+1), OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1), C≡CHC_(n)H_(2n+1), Ar₁, Ar₁—Ar₂, C_(n)H_(2n)—Ar₁, or no substitution, wherein Ar₁ and Ar₂ are independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof, and n is from 1 to 10.

In one embodiment, the host has the formula

In another embodiment, the host is selected from the group consisting of

and combinations thereof.

In one embodiment, the host is a metal complex.

Cyclometallated tetradentate Pt(II) compounds comprising an imidazole ring with a twisted aryl group are provided. The compounds have the formula:

Ring A, ring B, ring C and ring D are each independently a 5- or 6-membered carbocyclic or heterocyclic ring. L₁ and L₂ are independently selected from the group consisting of a single bond, BR, NR, O, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. n₁ is 0 or 1. n₂ is 0 or 1, n₁+n₂ is at least equal to 1. Z₁ and Z₂ are independently a nitrogen atom or a carbon atom. R₁, R₂, R₃, R₄, and R₇ may represent mono-, di-, tri-, or tetra-substitutions. R₁ is optionally fused to ring A. R₃ is optionally fused to ring B. R₄ is optionally fused to ring C. R₇ is optionally fused to ring D. R₃ and R₄ are optionally joined to form into a ring. At least one of ring B and ring C is a 5-membered carbocyclic or heterocyclic ring. R₁, R₂, R₃, R₄, R₅, R₆, and R₇ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloakenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R₅ and R₆ is not hydrogen or deuterium.

In one aspect, at least one of R₅ and R₆ is an alkyl in another aspect, at least one of R₅ and R₆ is an alkyl containing at least 3 carbons. In yet another aspect, at least one of R₅ and R₆ is a cycloalkyl.

In one aspect, each of R₅ and R₆ is an aryl.

In one aspect, R₃ or R₄ is a substituted aryl. In another aspect, R₃ or R₄ is a 2,6-disubstituted aryl.

Preferably, R₃ or R₄ is

R′₁ and R′₂, are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R′₁ and R′₂ is not hydrogen or deuterium. D is 5-membered or 6-membered carbocyclic or heterocyclic ring that is optionally further substituted with R′₃. R′₃ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, the compound has the formula:

R₈ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In another aspect, the compound has the formula:

In yet another aspect, the compound has the formula:

R₈ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In a further aspect, the compound has the formula:

In another aspect, the compound has the formula:

R₈ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloakenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In yet another aspect, the compound has the formula:

R₈ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In another aspect, the compound has the formula:

In yet another aspect, the compound had the formula:

Specific examples of cyclometallated tetradentate Pt(II) compounds comprising an imidazole ring with a twisted aryl group are provided. In one aspect, the compound is selected from the group consisting of:

Additionally, a first device comprising an organic light emitting device is provided. The organic light emitting device further comprises an anode, a cathode, and an organic layer. The organic layer is disposed between the anode and the cathode, and it comprises a compound having the formula:

Ring A, ring B, ring C and ring D are each independently a 5- or 6-membered carbocyclic or heterocyclic ring. L₁ and L₂ are independently selected from the group consisting of a single bond, BR, NR, O, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. n₁ is 0 or 1. n₂ is 0 or 1. n₁+n₂ is at least equal to 1. Z₁ and Z₂ are independently a nitrogen atom or a carbon atom. R₁, R₂, R₃, R₄, and R₇ may represent mono-, di-, tri-, or tetra-substitutions. R₁ is optionally fused to ring A. R₃ is optionally fused to ring B. R₄ is optionally fused to ring C. R₇ is optionally fused to ring D. R₃ and R₄ are optionally joined to form into a ring. At least one of ring B and ring C is a 5-membered carbocyclic or heterocyclic ring. R₁, R₂, R₃, R₄, R₅, R₆, and R₇ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R₅ and R₆ is not hydrogen or deuterium.

The various specific aspects discussed above for compounds having Formula I′ are also applicable to a compound having Formula I′ that is used in the first device. In particular, specific aspects of ring A, ring B, ring C, ring D, L₁, L₂, n₁, n₂, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R′₁, R′₂, R′₃, Formulas II′-IX′, and Compounds 1′-65′ of the compound having Formula I′ are also applicable to a compound having Formula I′ that is used in a device.

In one aspect, the organic layer is an emissive layer and the compound is an emissive dopant.

In one aspect, the organic layer further comprises a host. In another aspect, the host comprises a triphenylene containing benzo-fused thiophene or benzo-fused furan, and any substituent in the host is an unfused substituent independently selected from the group consisting of C_(n)H_(2n+1), OC_(n)H_(2n+1), OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1), C≡CHC_(n)H_(2n+1), Ar₁, Ar₁—Ar₂, C_(n)H_(2n)—Ar₁, or no substitution. n is from 1 to 10. Ar₁ and Ar₂ are independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof.

In one aspect, the host has the formula:

In another aspect, the host is selected from the group consisting of:

and combinations thereof.

In yet another aspect, the host is a metal complex.

In one aspect, the organic layer is an emissive layer and the compound is a non-emissive dopant.

In one aspect, the first device is a consumer product. In another aspect, the first device is an organic light emitting device. In yet another aspect, the first device comprises a lighting panel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.

FIG. 3 shows a compound of Formula I.

FIG. 4 shows a compound of Formula I′.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from their singlet states (“fluorescence”) as disclosed, for example, in U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.

More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 151-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporated by reference in their entireties. Phosphorescence is described in more detail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference.

FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, and a cathode 160. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporated by reference.

More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an “inverted” OLED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2. For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties.

Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. patent application Ser. No. 10/233,470, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and OVJD. Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processability than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention may be incorporated into a wide variety of consumer products, including flat panel displays, computer monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, vehicles, a large area wall, theater or stadium screen, or a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C., and more preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, aryalkyl, heterocyclic group, aryl, aromatic group, and heteroaryl are known to the art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32, which are incorporated herein by reference.

A compound having the formula:

is provided, wherein G has the structure

and wherein G is fused to any two adjacent carbon atoms on ring A. Ring B, ring C, and ring D are 5- or 6-membered carbocyclic or heterocyclic aromatic rings. L₁, L₂, and L₃ are independently selected from the group consisting of a single bond, BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. At least one of L₁, L₂, and L₃ is not a single bond, and X is selected from the group consisting of BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. Z₁, Z₂, Z₃, and Z₄ are nitrogen or carbon atoms, and A₁, A₂, A₃, A₄, A₅, A₆, A₇, and A₈ comprise carbon or nitrogen. R₁, R₂, R₃, and R₄ independently represent mono-, di-, tri-, or tetra-substitution, wherein R₁ is optionally fused, R₂ is optionally fused to ring B, R₃ is optionally fused to ring C, and R₄ is optionally fused to ring D. R₃ and R₄ are optionally linked to form a ring. If L₂ is not a single bond, R₃ and L₂ or R₄ and L₂ are optionally linked to form a ring. R, R′, R₁, R₂, R₃, and R₄ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one embodiment, the compound has a neutral charge. In one embodiment, the platinum center in the compounds of Formula I is platinum(II). In one embodiment, at least two of Z₁, Z₂, Z₃, and Z₄ are nitrogen atoms. In another embodiment, at least two of Z₁, Z₂, Z₃, and Z₄ are carbon atoms.

In one embodiment, at least one of ring B, ring C, and ring D comprises a carbene ligand coordinated to Pt. In another embodiment, at least one of Z₁, A₁, A₂, A₃, A₄, A₅, A₆, A₇, and A₈ is a nitrogen atom.

In one embodiment, the compound has the formula:

In the compound of Formula II, L₁ and the bond to the platinum atom can be on any two adjacent atom centers on the illustrated dibenzo ring system.

In another embodiment, the compound has the formula:

In one embodiment, the compound has the formula:

In the compound of Formula IV, L₁ and the bond to the platinum atom can be on any two adjacent atom centers on the illustrated dibenzo ring system (i.e. ring system bearing the X fragment, which is also referred to herein as DBX). Similarly, L₂ and the bond to the platinum atom can be on any two adjacent atom centers on the illustrated dibenzo ring system (i.e. ring system bearing the Y fragment, which is also referred to herein as DBY). Y is selected from the group consisting of BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′.

In another embodiment, the compound has the formula:

In one embodiment, L₁ and L₂ are single bonds. In another embodiment, L₃ is independently selected from the group consisting of O, S, and NR. In another embodiment, L₃ is NR, and R is phenyl or substituted phenyl. In one embodiment, L₃ is O.

In one embodiment, Z₂ and Z₃ are nitrogen atoms. In another embodiment, Z₂ and Z₄ are nitrogen atoms. In one embodiment, X is independently selected from the group consisting of O, S, and NR. In one embodiment, X is O.

In one embodiment, the compound is selected from the group consisting of:

wherein Y is selected from the group consisting of BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. A₁′, A₂′, A₃′, A₄′, A₅′, A₆′, A₇′, and A₈′ comprise carbon or nitrogen. At most one of A₁, A₂, A₃, A₄ is nitrogen, and at most one of A₁′, A₂′, A₃′, A₄′ is nitrogen. At most one of A₅, A₆, A₇, A₈ is nitrogen, and the nitrogen is not bound to Pt. At most one of A₅′, A₆′, A₇′, A₈′ is nitrogen, and the nitrogen is not bound to Pt. The Pt forms at least two Pt—C bonds and R₃ and R₄ may be fused together to form a ring. R₅ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one embodiment, the compounds of Formula I include:

In Compounds 1-186, when R is present it can be hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, aryl, heteroaryl, acyl and combinations thereof.

A first device is provided. The first device comprises a first organic light emitting device, further comprising an anode, a cathode, and an organic layer, disposed between the anode and the cathode, comprising a compound having the formula:

is provided, wherein G has the structure

and wherein G is fused to any two adjacent carbon atoms on ring A. Ring B, ring C, and ring D are 5- or 6-membered carbocyclic or heterocyclic aromatic rings. L₁, L₂, and L₃ are independently selected from the group consisting of a single bond, BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. At least one of L₁, L₂, and L₃ is not a single bond, and X is selected from the group consisting of BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′, Z₁, Z₂, Z₃, and Z₄ are nitrogen or carbon atoms, and A₁, A₂, A₃, A₄, A₅, A₆, A₇, and A₈ comprise carbon or nitrogen, R₁, R₂, R₃, and R₄ independently represent mono-, di-, tri-, or tetra-substitution, wherein R₁ is optionally fused, R₂ is optionally fused to ring B, R₃ is optionally fused to ring C, and R₄ is optionally fused to ring D. R, R′, R₁, R₂, R₃, and R₄ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one embodiment, the first device is a consumer product. In another embodiment, the first device is an organic light-emitting device. In one embodiment, the first device comprises a lighting panel. In one embodiment, the organic layer is an emissive layer and the compound is an emissive dopant. In another embodiment, the organic layer is an emissive layer and the compound is a non-emissive dopant.

In one embodiment, the organic layer further comprises a host. In another embodiment, the host comprises a triphenylene containing benzo-fused thiophene or benzo-fused furan, wherein any substituent in the host is an unfused substituent independently selected from the group consisting of C_(n)H_(2n+1), OC_(n)H_(2n+1), OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1), C≡CHC_(n)H_(2n+1), Ar₁, Ar₁—Ar₂, C_(n)H_(2n)—Ar₁, or no substitution, wherein Ar₁ and Ar₂ are independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof, and n is from 1 to 10.

In one embodiment, the host has the formula

In another embodiment, the host is selected from the group consisting of

and combinations thereof.

In one embodiment, the host is a metal complex.

A novel class of tetradentate platinum (II) compounds are provided (as illustrated in FIG. 4). The compounds comprise: (i) two ligands that each contain at least one 5-membered carbocyclic or heterocyclic ring, (ii) one of the ligands comprises an imidazole ring with a twisted aryl group attached at N−1, and (iii) in the same ligand as the imidazole, a 6-membered carbocyclic or heterocyclic ring that is attached to the platinum via a carbon atom. These properties, taken together, may make the compounds particularly suitable for use in an OLED.

Although the first demonstrated PHOLED contained a platinum complex, namely 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum (II) (PtOEP), platinum complexes have not found any practical use in state-of-the-art PHOLEDs. (Nature, 1998, 395, 151). Compared to iridium complexes, platinum(II) complexes generally have a relatively long excited state lifetime and a lower quantum yield. In addition, platinum (II) complexes adopt a square planar geometry, which often causes excimer formation. Therefore, these complexes may have broadened emission spectrum at higher doping concentration in an OLED.

Bidentate and tridentate Pt (II) complexes have been reported, but, generally, these compounds have limited application in OLEDs. These complexes often have poor thermal stability and device stability, thereby limiting their application in OLEDs.

Tetradentate Pt(II) complexes have also been disclosed in literature, but, similar to the bidentate and tridentate Pt(II) complexes, these tetradentate Pt(II) complexes may have limited use in OLEDs.

As discussed above, the tetradentate platinum (II) complexes provided herein have several beneficial characteristics. First, the compounds comprise two ligands that each contain a 5-membered carbocyclic or heterocyclic ring. The first ligand comprises an imidazole ring and ring A. The second ligand comprises ring B and ring C, and one of ring B and ring C must be a 5-membered carbocyclic or heterocyclic ring. The other of ring B and ring C may be either a 5 or 6-membered carbocyclic or heterocyclic ring. Preferably, ring A and one of ring B and ring C is a 6-membered carbocyclic or heterocyclic ring, i.e., each ligand contains one 5-membered ring and one 6-membered ring. Without being bound by theory, it is believed that the basic ligand structure may be used to tune the energy levels and improve triplet energy because a 5-membered ring generally has a higher triplet energy than a 6-membered ring.

Second, a ligand contains an imidazole ring with a twisted aryl attached to N−1 of the imidazole (illustrated in FIG. 4). By incorporating a twisted aryl moiety into the tetradentate architecture, the Pt(II) complexes may demonstrate higher stability and, thus, provide longer device lifetimes. Without being bound by theory, it is believed that twisting the aryl group out of the plane of the imidazole ring, thus breaking the conjugation and making the compound less planar, may result in bluer emission, improved sublimation and improved efficiency. Specifically, the compounds may be less prone to triplet-triplet annihilation and self-quenching, because they have more three-dimensional character.

Third, ring A of the first ligand is attached to the platinum via a carbon atom. Without being bound by theory, it is believed that such a ligand system may provide high triplet.

Taken together, the features of these compounds may provide beneficial properties that make these compounds particularly suitable for use in OLEDs. For example, the compounds may provide improved blue emission, improved stability and improved efficiency.

Cyclometallated tetradentate Pt(II) compounds comprising an imidazole ring with a twisted aryl group are provided. The compounds have the formula:

Ring A, ring B, ring C and ring D are each independently a 5- or 6-membered carbocyclic or heterocyclic ring. L₁ and L₂ are independently selected from the group consisting of a single bond, BR, NR, O, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. n₁ is 0 or 1. n₂ is 0 or 1. n₁+n₂ is at least equal to 1. Z₁ and Z₂ are independently a nitrogen atom or a carbon atom. R₁, R₂, R₃, R₄, and R₇ may represent mono-, di-, tri-, or tetra-substitutions. R₁ is optionally fused to ring A. R₃ is optionally fused to ring B. R₄ is optionally fused to ring C. R₇ is optionally fused to ring D. R₃ and R₄ are optionally joined to form into a ring. At least one of ring B and ring C is a 5-membered carbocyclic or heterocyclic ring. R₁, R₂, R₃, R₄, R₅, R₆, and R₇ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R₅ and R₆ is not hydrogen or deuterium.

When n₁ or n₂ is equal to 0, there is no connection, i.e., no single bond or other substitution at L₁ or L₂. Compounds 1′-3′ are non-limiting examples of compounds where n₁ is 0. Alternatively, Compounds 26′-28′ are non-limiting examples of compounds where n₂ is 0.

In one embodiment, at least one of R₅ and R₆ is an alkyl. In another aspect, at least one of R₅ and R₆ is an alkyl containing at least 3 carbons. In yet another aspect, at least one of R₅ and R₆ is a cycloalkyl.

In one embodiment, each of R₅ and R₆ is an aryl.

In one embodiment, R₃ or R₄ is a substituted aryl. In another embodiment, R₃ or R₄ is a 2,6-disubstituted aryl.

Preferably, R₃ or R₄ is

R′₁ and R′₂ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R′₁ and R′₂ is not hydrogen or deuterium. D is 5-membered or 6-membered carbocyclic or heterocyclic ring that is optionally further substituted with R′₃. R′₃ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, the compound has the formula:

R₈ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In another embodiment, the compound has the formula:

In yet another embodiment, the compound has the formula:

R₈ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In a further embodiment, the compound has the formula:

In another embodiment, the compound has the formula:

R₈ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In yet another embodiment, the compound has the formula:

R₈ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In another embodiment, the compound has the formula:

In yet another embodiment, the compound has the formula:

Specific examples of cyclometallated tetradentate Pt(II) compounds comprising an imidazole ring with a twisted aryl group are provided. In one aspect, the compound is selected from the group consisting of:

Additionally, a first device comprising an organic light emitting device is provided. The organic light emitting device further comprises an anode, a cathode, and an organic layer. The organic layer is disposed between the anode and the cathode, and it comprises a compound having the formula:

Ring A, ring B, ring C and ring D are each independently a 5- or 6-membered carbocyclic or heterocyclic ring. L₁ and L₂ are independently selected from the group consisting of a single bond, BR, NR, O, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′. n₁ is 0 or 1. n₂ is 0 or 1. n₁+n₂ is at least equal to 1. Z₁ and Z₂ are independently a nitrogen atom or a carbon atom. R₁, R₂, R₃, R₄, and R₇ may represent mono-, di-, tri-, or tetra-substitutions. R₁ is optionally fused to ring A. R₃ is optionally fused to ring B. R₄ is optionally fused to ring C. R₇ is optionally fused to ring D. R₃ and R₄ are optionally joined to form into a ring. At least one of ring B and ring C is a 5-membered carbocyclic or heterocyclic ring. R₁, R₂, R₃, R₄, R₅, R₆, and R₇ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. At least one of R₅ and R₆ is not hydrogen or deuterium.

The various specific embodiments discussed above for compounds having Formula I′ are also applicable to a compound having Formula I′ that is used in the first device. In particular, specific aspects of ring A, ring B, ring C, ring D, L₁, L₂, n₁, n₂, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R′₁, R′₂, R′₃, Formulas II′-IX′, and Compounds 1′-65′ of the compound having Formula I′ are also applicable to a compound having Formula I′ that is used in a device.

In one embodiment, the organic layer is an emissive layer and the compound is an emissive dopant.

In one embodiment, the organic layer further comprises a host. In another embodiment, the host comprises a triphenylene containing benzo-fused thiophene or benzo-fused furan, and any substituent in the host is an unfused substituent independently selected from the group consisting of C_(n)H_(2n+1), OC_(n)H_(2n+1), OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1), C≡CHC_(n)H_(2n+1), Ar₁, Ar₁—Ar₂, C_(n)H_(2n)—Ar₁, or no substitution. n is from 1 to 10. Ar₁ and Ar₂ are independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof.

In one embodiment, the host has the formula:

In another embodiment, the host is selected from the group consisting of:

and combinations thereof.

In yet another embodiment, the host is a metal complex.

In one embodiment, the organic layer is an emissive layer and the compound is a non-emissive dopant.

In one embodiment, the first device is a consumer product. In another embodiment, the first device is an organic light emitting device. In yet another embodiment, the first device comprises a lighting panel.

Device Examples

All device examples were fabricated by high vacuum (<10-7 Torr) thermal evaporation (VTE). The anode electrode is 800 Å or 1200 Å of indium tin oxide (ITO). The cathode consisted of 10 Å of LiF followed by 1000 Å of Al. All devices were encapsulated with a glass lid sealed with an epoxy resin in a nitrogen glove box (<1 ppm of H₂O and O₂) immediately after fabrication, and a moisture getter was incorporated inside the package.

In some devices, the organic stack of the devices consisted of sequentially, from the ITO surface, 100 Å of Compound A as the hole injection layer (HIL), 300 Å of 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD) as the hole transporting later (HTL), 300 Å of Compound B doped with Compound 4 as the emissive layer (EML), 50 Å of Compound B as BL, and 450 Å of Alq as the ETL. Comparative Device Examples were fabricated in a manner similar to that of the Device Examples, except that Compound X was used as the emitter instead of Compound 4. The device results and data are summarized in Tables 1 and 2 from those devices. As used herein, Compound A, Compound B, Alq, α-NPD, and Compound X have the following structures:

In some devices, the organic stack of the devices consisted of sequentially, from the ITO surface, 100 Å of LG101 (purchased from LG Chem) as the hole injection layer (HIL), 300 Å of either NPD or TAPC as the hole transporting layer (HTL), 300 Å of UGH3 doped with the emitter at either 15% or 20% as the emissive layer (EML), 50 Å of Compound B′ as blocking layer (BL), and 300 Å of Alq or 3TPYMB as the electron transporting layer (ETL).

As used herein, the following compounds have the following structures:

The device examples are detailed in Table 3, and the corresponding device data is summarized in Table 4.

TABLE 1 VTE Phosphorescent OLEDs Example HIL HTL EML (doping %) BL ETL Example 1 Compound A NPD Compound B Compound 4 Compound B Alq 20% Comparative compound A NPD Compound B Compound X Compound B Alq Example 1 15%

TABLE 2 VTE Device Data At 1000 nits At 40 mA/cm² 1931 CIE FWHM Voltage LE EQE PE L₀ LT80% Example x y λ_(max) (nm) (V) (Cd/A) (%) (lm/W) (nits) (h) Example 1 0.422 0.552 538 64 8.4 10.6 4.0 4.0 2001 145 Comparative 0.357 0.581 514 60 9.7 8.2 2.8 2.7 2989 58 Example 1

LED devices incorporating compounds of Formula have demonstrated superior properties. As a merely illustrative example, Example 1, which incorporates Compound 4 containing a dibenzofuran moiety, has a higher efficiency (10.6 Cd/A, 4.0% EQE, 4.0 lm/W) than the Comparative Example, which uses Compound X, lacking any dibenzo (DBX) fragment (9.7 Cd/A, 2.8% EQE, 2.7 lm/W). Devices incorporating Compound 4 also demonstrated a longer lifetime (145 h) in comparison to Compound X (58 h) and a lower turn-on voltage (8.4 V) versus the Comparative Example (9.7 V). These results indicate that incorporating compounds of Formula I, which bear one or more DBX groups, results in devices with highly desirable properties.

TABLE 3 VTE PHOLEDs Example HIL HTL EML doping % BL ETL 1 LG101 TAPC 15 Compound B′ 3TPYMB 2 LG101 NPD 15 Compound B′ Alq 3 LG101 TAPC 20 Compound B′ Alq

TABLE 4 VTE Device Data At 1000 nits 40 mA/cm² 1931 CIE λ_(max) FWHM Voltage LE EQE PE Lo Example X Y (nm) (nm) (V) (Cd/A) (%) lm/W (nits) 1 0.126 0.169 468 14 8.3 15.1 12.3 5.7 2,824 2 0.127 0.176 468 14 6.5 11.6 9.2 5.6 2,116 3 0.13 0.196 470 18 7.6 14.5 10.6 6 2,692

DFT calculations were used to predict the properties of inventive compounds and comparative compounds. The HOMO, LUMO, the HOMO-LUMO energy gap and triplet energies for each structure were calculated using DFT calculations with the Gaussian software package at the B3LYP/cep-31g functional and basis set. The DFT calculations are summarized in Table 5. Ex. is an abbreviation for Example.

TABLE 5 DFT Data Ex. Structure HOMO (eV) LUMO (eV) Gap (eV) T₁ (nm) 4

−4.54 −0.97 −3.57 452 Compound 1′ 5

−4.05 −0.90 −3.15 486 Compound 2′ 6

−4.04 −0.74 −3.31 493 Compound 3′ 7

−4.17 −0.94 −3.22 507 Compound 4′ 8

−4.31 −1.04 −3.27 531 Compound 5′ 9

−4.59 −0.99 −3.60 496 Compound 6′ 10

−4.04 −1.43 −2.61 537 Compound 7′ 11

−4.78 −1.65 −3.13 567 Comparitive Compound 1′ 12

−4.55 −1.67 −2.88 566 Comparative Compound 2′ 13

−4.09 −1.21 −2.88 527 Comparative Compound 3′ 14

−4.08 −1.57 −2.51 589 Comparative Compound 4′ 15

−4.45 −2.24 −2.21 755 Comparative Compound 5′

Table 5 shows HOMO, LUMO energy levels, the HOMO-LUMO energy gap and triplet energies for a series of imidazole Pt (II) compounds comprising two ligands that each contain a 5-membered carbocyclic or heterocyclic ring, i.e., Compounds 1′-6′, in comparison to compounds comprising only one ligand with a 5-membered carbocyclic or heterocyclic ring, i.e., Comparative Compounds 1′ and 2′. The most common aromatic six member ring that coordinates neutrally in emissive organometallic compounds is pyridine. It can be seen in this table that replacing a six member ring with a five member heterocyclic ring offers advantages with regards to tuning the energy levels and triplet energy. For example, Comparative Compound 1′ with pyridine is predicted to have a LUMO energy of −1.65 eV and a triplet of 567 nm. In all cases, when pyridine is replaced by a five member heterocyclic ring, such as imidazole, pyrazole, and imidazole-carbene, it results in a higher energy LUMO and triplet allowing for compounds with desirable blue emission.

Comparative Compounds 3′ and 4′ are analogous to the twisted aryl inventive Compound 2′ and Compound 7′. From the data, it can be seen that compounds lacking a twisted aryl have significantly lower triplet energy, which is thought to be due to increased delocalization on the N-aryl substituent. For example, Compound 2′ is calculated to have a triplet wavelength of 486 nm compared to 527 nm for Comparative Compound 3′. The effect of further delocalization on the N-aryl substituent can be minimized by employing a twisted aryl. For example, Compound 7′ has a triplet wavelength of 537 nm, compared to the corresponding non-twisted compound, Comparative Compound 4′, which has a triplet wavelength of 589 nm.

Comparative Compound 5′ shows a tetradentate compounds with ligands similar to the inventive compounds, but ring A is bound to the platinum via a nitrogen atom. Specifically, Comparative Compound 5′ contains a first ligand having a twisted aryl imidazole and a neutral pyridine, i.e., ring A, and a second ligand having an anionic imidazole and a benzene. Conversely, both 5-membered rings in the inventive compounds are neutrally bound nitrogen chelates, e.g., imidazole, and the 6-membered rings are anionic carbon chelates, e.g., phenyl. From the data, it can be seen that the inventive compounds may provide high triplet emission. For example, Comparative Compound 5′ is predicted by calculation to have a profoundly low triplet energy of 755 nm.

Based on DFT calculations, the triplet transition of Comparative Compound 5′ may be based on an intra-ligand charge transfer transition (ILCT) from one side of the ligand bridged by oxygen to the other. The HOMO for Comparative Compound 5′ is localized predominantly on the 5-member ring anionic nitrogen chelate and phenyl ring, and the LUMO is localized on the neutrally coordinated pyridine and imidazole. Therefore, the photophysical properties of compounds having ring A bound to the platinum via a nitrogen atom may be very different than the typical metal-ligand charge transfer (MLCT) character predicted for the inventive compounds. For example, the calculated LUMO of Comparative Compound 5′ is −2.24 eV, while the calculated LUMO of Compound 1′ is −0.97 eV. Therefore, the coordination of ring A to the platinum via a nitrogen atom may result in a large and undesirable lowering of the triplet energy. Alternatively, the inventive compounds, in which ring A coordinates to the platinum via a carbon atom, may have a high triplet energy.

Combination with Other Materials

The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a wide variety of other materials present in the device. For example, emissive dopants disclosed herein may be used in conjunction with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The materials described or referred to below are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in the present invention is not particularly limited, and any compound may be used as tong as the compound is typically used as a hole injecting/transporting material. Examples of the material include, but not limit to: a phthalocyanine or porphyrin derivative; an aromatic amine derivative; an indolocarbazole derivative; a polymer containing fluorohydrocarbon; a polymer with conductivity dopants; a conducting polymer, such as PEDOT/PSS; a self-assembly monomer derived from compounds such as phosphonic acid and sliane derivatives; a metal oxide derivative, such as MoO_(x); a p-type semiconducting organic compound, such as 1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and a cross-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, but not limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; group consisting aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each Ar is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one embodiment, Ar¹ to Ar⁹ is independently selected from the group consisting of:

k is an integer from 1 to 20; X¹ to X⁸ is C (including CH) or N; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but not limit to the following general formula:

M is a metal, having an atomic weight greater than 40; (Y¹—Y²) is a bidentate ligand, Y¹ and Y² are independently selected from C, N, O, P, and S; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and m+n is the maximum number of ligands that may be attached to the metal.

In one embodiment, (Y¹—Y²) is a 2-phenylpyridine derivative.

In another embodiment, (Y¹—Y²) is a carbene ligand.

In another embodiment, M is selected from Ir, Pt, Os, and Zn.

In a further embodiment, the metal complex has a smallest oxidation potential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Host:

The light emitting layer of the organic EL device of the present invention preferably contains at least a metal complex as light emitting material, and may contain a host material using the metal complex as a dopant material. Examples of the host material are not particularly limited, and any metal complexes or organic compounds may be used as long as the triplet energy of the host is larger than that of the dopant.

Examples of metal complexes used as host are preferred to have the following general formula:

M is a metal; (Y³—Y⁴) is a bidentate ligand, Y³ and Y⁴ are independently selected from C, N, O, P, and S; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and m+n is the maximum number of ligands that may be attached to the metal.

In one embodiment, the metal complexes are:

(O—N) is a bidentate having metal coordinated to atoms O and N.

In another embodiment, M is selected from Ir and Pt.

In a further embodiment, (Y³—Y⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the group consisting aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; group consisting aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atome, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each group is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one embodiment, host compound contains at least one of the following groups in the molecule:

R¹ to R⁷ is independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from C (including CH) or N.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holes and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED.

In one embodiment, compound used in HBL contains the same molecule used as host described above.

In another embodiment, compound used in HBL contains at least one of the following groups in the molecule:

k is an integer from 0 to 20; L is an ancillary ligand, m is an integer from 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable of transporting electrons. Electron transport layer may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. Examples of the ETL material are not particularly limited, and any metal complexes or organic compounds may be used as long as they are typically used to transport electrons.

In one embodiment, compound used in ETL contains at least one of the following groups in the molecule:

R¹ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above.

Ar¹ to Ar³ has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from C (including CH) or N.

In another embodiment, the metal complexes used in ETL contains, but not limit to the following general formula:

(O—N) or (N—N) is a bidentate ligand, having metal coordinated to atoms O, N or N, N; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal.

In any above-mentioned compounds used in each layer of the OLED device, the hydrogen atoms can be partially or fully deuterated.

In addition to and/or in combination with the materials disclosed herein, many hole injection materials, hole transporting materials, host materials, dopant materials, exiton/hole blocking layer materials, electron transporting and electron injecting materials may be used in an OLED. Non-limiting examples of the materials that may be used in an OLED in combination with materials disclosed herein are listed in Table 6 below. Table 6 lists non-limiting classes of materials, non-limiting examples of compounds for each class, and references that disclose the materials.

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EXPERIMENTAL

Chemical abbreviations used throughout this document are as follows: Cy is cyclohexyl, dba is dibenzylideneacetone, EtOAc is ethyl acetate, DME is dimethoxyethane, dppf is 1,1′-bis(diphenylphosphino)ferrocene, S-Phos is dicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine,

Synthesis of 6-bromo-N-(6-bromopyridin-2-yl)-N-phenylpyridin-2-amine

To a 500 mL 3-neck round-bottom flask was added 2,6-dibromopyridine (20 g, 84 mmol), aniline (3.1 mL, 33.8 mmol), dppf (0.749 g, 1.351 mmol), sodium t-butoxide (8.11 g, 84 mmol), and 250 mL toluene. Nitrogen was bubbled directly into the reaction mixture. Pd₂(dba)₃ (0.62 g, 0.68 mmol) was added to the reaction mixture which was heated to reflux overnight. The reaction mixture was cooled and diluted with ethyl acetate and water and tittered through Celite® to remove insoluble material. The layers were separated and the aqueous layer extracted with ethyl acetate. The organic layers were washed with brine, dried over magnesium sulfate, filtered, and evaporated. The residue was purified by column chromatography eluting with dichloromethane to give 6-bromo-N-(6-bromopyridin-2-yl)-N-phenylpyridin-2-amine (6.3 g, 46%).

6-Bromo-N-(6-bromopyridin-2-yl)-N-phenylpyridin-2-amine (7 g, 17.3 mmol), phenylboronic acid (5.3 g, 43.2 mmol), Pd₂(dba)₃ (0.32 g, 0.35 mmol), dicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine (0.57 g, 1.38 mmol), potassium phosphate tribasic monohydrate (11.94 g, 51.8 mmol), toluene (200 mL) and water (20 mL) were added to a flask and degassed with nitrogen. The reaction mixture was heated to reflux for 16 h before being cooled to room n temperature. Water was added and the layers separated, washing the aqueous twice with EtOAc and combined organics with water and brine. After removal of the solvent, the crude product was chromatographed on silica gel with 9/1 (v/v) hexane/EtOAc to give 5.6 g of a white solid, which was recrystallized from hexane to give 5.1 g of pure (HPLC purity: 100%) product as confirmed by NMR and GC/MS.

Synthesis of 6-bromo-N-phenyl-N-(6-phenylpyridin-2-yl)pyridine-2-amine

To a 1 L 3-neck round-bottom flask was added 6-bromo-N-(6-bromopyridin-2-yl)-N-phenylpyridin-2-amine (5.3 g, 13.08 mmol), phenylboronic acid (1.595 g, 13.08 mmol), potassium carbonate (5.42 g, 39.3 mmol), 200 mL dimethoxyethane and 100 mL water. Nitrogen was bubbled directly into the mixture. Pd(PPh₃)₄ (0.151 g, 0.131 mmol) was added and the reaction mixture was heated to 105° C. overnight under nitrogen. The reaction mixture was diluted with ethyl acetate and water. The layers were separated and the aqueous layer extracted with ethyl acetate. The organic layers were dried over magnesium sulfate, filtered, and evaporated leaving a yellow oil. The material was purified by column chromatography using a reverse phase column eluting with 80/20 (v/v) acetonitrile/water to give 6-bromo-N-phenyl-N-(6-phenylpyridin-2-yl)pyridine-2-amine (2.84 g, 45%).

Synthesis of 6-(dibenzo[b,d]furan-4-yl)-N-phenyl-N-(6-phenylpyridin-2-yl)pyridine-2-amine: To a 300 mL 3-neck flask was added 6-bromo-N-phenyl-N-(6-phenylpyridin-2-yl)pyridin-2-amine (2.5 g, 6.21 mmol), dibenzo[b,d]furan-4-ylboronic acid (1.6 g, 7.5 mmol), potassium phosphate, monohydrate (4.3 g, 18.6 mmol), dicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine (S-Phos) (0.102 g, 0.249 mmol), 100 mL toluene, and 10 mL water. Nitrogen was bubbled directly into the mixture. Pd₂(dba)₃ (0.057 g, 0.062 mmol) was added and the reaction mixture heated to reflux overnight under nitrogen. Water was added to the reaction mixture and the layers were separated. The aqueous layer was extracted with ethyl acetate. The organic layers were washed with brine, dried over magnesium sulfate, filtered, evaporated. The material was purified by column chromatography eluting with 8/2/2.5 hexane/dichloromethane/ethyl acetate to give 6-(dibenzo[b,d]furan-4-yl)-N-phenyl-N-(6-phenylpyridin-2-yl)pyridine-2-amine (2.7 g, 88%).

Synthesis of 6-(dibenzo[b,d]furan-4-yl)-N-(6-(dibenzo[b,d]furan-4-yl)pyridin-2-yl)-N-phenylpyridin-2-amine

To a 500 mL 3-neck round-bottom flask was added 6-bromo-N-(6-bromopyridin-2-yl)-N-phenylpyridin-2-amine (4.4 g, 10.9 mmol), dibenzo[b,d]furan-4-ylboronic acid (5.1 g, 23.9 mmol), Pd₂(dba)₃ (0.10 g, 0.11 mmol), dicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine (0.18 g, 0.43 mmol), and potassium phosphate tribasic monohydrate (12.5 g, 54.3 mmol) in toluene (100 mL) and water (10 mL). Nitrogen was bubbled directly into the reaction mixture for 20 min. and the reaction heated to reflux for 16 h. The reaction mixture was cooled and diluted with ethyl acetate and water and filtered through Celite to remove insoluble material. The layers were separated and the aqueous layer extracted with dichloromethane. The organic layers were washed with brine, dried over magnesium sulfate, filtered, and evaporated. The residue was purified by column chromatography eluting with 95/5 dichloromethane/ethyl acetate to give 2.1 g (87%) of 6-(dibenzo[b,d]furan-4-yl)-N-(6-(dibenzo[b,d]furan-4-yl)pyridin-2-yl)-N-phenylpyridin-2-amine as a white solid. The product was confirmed by LC/MS, NMR and HPLC (purity: 99.96%).

Synthesis of Compound X

N,6-Diphenyl-N-(6-phenylpyridin-2-yl)pyridin-2-amine (1.9 g, 4.8 mmol) and potassium tetrachloroplatinate (1.97 g, 4.8 mmol) were mixed in 100 mL of acetic acid. The mixture was degassed with nitrogen sparge for 20 min. and heated to 140° C. for 4 days. After cooling, water was added and the solid was collected by filtration. The solid was washed of the fit with dichloromethane to give a yellow filtrate that was dried over sodium sulfate and the solvent removed. The crude product was purified by column on silica using dichloromethane as solvent to give 1.1 g of the platinum complex. The complex was sublimed (260° C. 10⁻⁵ Torr) to give 0.8 g of Compound X as a yellow solid (HPLC purity: 99.3%) as confirmed by NMR and LC/MS.

Synthesis of Compound 4

To a 300 mL 3-neck round bottom flask was added K₂PtCl₄ (2.1 g, 5.0 mmol), 6-(dibenzo[b,d]furan-4-yl)-N-phenyl-N-(6-phenylpyridin-2-yl)pyridin-2-amine (2.7 g, 5.5 mmol), and 100 mL acetic acid. The reaction mixture was purged with nitrogen for 20 minutes. The reaction mixture was heated to 140° C. under nitrogen for 3 days, cooled, and diluted with hexane. A green solid was filtered of and washed with hexane. The material was purified by column chromatography eluting with 60/40 to 70/40 (v/v) dichloromethane/hexane followed by sublimation overnight at 300° C. to yield 0.58 g (17%) of Compound as a yellow solid. The product was confirmed by LC/MS and HPLC (99.1% pure).

Synthesis of Compound 13

6-(Dibenzo[b,d]furan-4-yl)-N-(6-(dibenzo[b]furan-4-yl)pyridin-2-yl)-N-phenylpyridin-2-amine (1.8 g, 3.1 mmol) and K₂PtCl₄ (1.3 g, 3.1 mmol) were mixed in 100 mL of acetic acid. The mixture was bubbled with nitrogen for 20 min. before being heated to 140° C. for 4 days. After cooling, water was added and the solid collected by filtration. The solid was washed with dichloromethane to give a yellow filtrate that was concentrated to give a yellow solid. The solid was suspended in dichloromethane and methanol was added to give a precipitate that was filtered and washed with methanol and hexane and dried to give 0.88 g (37%) of Compound 13 as an orange solid. The product was confirmed by LC/MS and HPLC (99.1% pure).

Example 1 Synthesis of Compound 1′

Synthesis of 4-(3-chlorophenyl)-1H-imidazole

2-bromo-1-(3-chlorophenyl)ethanone (20.15 g, 86 mmol) in 80 mL formamide was placed into a 250 mL round-bottomed flask, and the reaction mixture was heated to 165° C. for 2.5 h. The reaction was then cooled and the solid was filtered and washed with water. The filtrate was basified to pH 12, and extracted with ethyl acetate. The organic layer was combined with the crude solid, and chromatographed on silica gel with 3-5% MeOH in DCM to obtain 10.9 g (71%) of 4-(3-chlorophenyl)-1H-imidazole as a solid.

Synthesis of 4-(3-chlorophenyl)-1-(2,6-dimethylphenyl)-1H-imidazole

A pressure flask was charged with 4-(3-chlorophenyl)-1H-imidazole (10.82 g, 60.6 mmol) and 2-iodo-1,3-dimethylbenzene (16.87 g, 72.7 mmol). The reaction mixture was diluted with DMF (60 mL), and copper(I) iodide (1.1 g, 6.1 mmol), N,N-dimethylethane-1,2-diamine (2.6 nit, 24.2 mmol) and cesium carbonate (23.68 g, 72.7 mmol) were added. After degassing with nitrogen, the reaction mixture was stirred in an oil bath at 160° C. for 48 h before being diluted with ethyl acetate and filtered through celite. The filtrate was washed with aqueous LiCl, brine and water. The product was purified by chromatography on silica gel with 0-5% EtOAc in DCM to afford 3.8 g (22%) of 4-(3-chlorophenyl)-1-(2,6-dimethylphenyl)-1H-imidazole.

Synthesis of 3-(1-(2,6-dimethylphenyl)-1H-imidazol-4-yl)-N-(3-(1-(2,6-dimethylphenyl)-1H-imidazol-4-yl)phenyl)-N-phenylaniline

4-(3-chlorophenyl)-1-(2,6-dimethylphenyl)-1H-imidazole (5.4 g, 19.1 mmol) and aniline (0.87 mL, 9.5 mmol) in toluene (200 mL) were placed in a 500 mL round-bottomed flask. Sodium tert-butoxide (4.0 g, 41.9 mmol) and dicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine (0.783 g, 1.906 mmol) were added, and the reaction mixture was degassed before Pd₂(dba)₃ (0.44 g, 0.48 mmol) was added. This was evacuated and backfilled with nitrogen. The reaction was stirred at reflux for 24 h. The mixture was then filtered through celite. Next, the filtrate was concentrated and chromatographed on silica gel with 10-25% ethyl acetate in hexane followed by 10% ethyl acetate in DCM to obtain 2.8 g (51%) of 3-(1-(2,6-dimethylphenyl)-1H-imidazol-4-yl)-N-(3-(1-(2,6-dimethylphenyl)-1H-imidazol-4-yl)phenyl)-N-phenylaniline as a white solid.

Synthesis of the Compound 1′

3-(1-(2,6-dimethylphenyl)-1H-imidazol-4-yl)-N-(3-(1-(2,6-dimethylphenyl)-1H-imidazol-4-yl)phenyl)-N-phenylaniline (1.7 g, 2.9 mmol) and potassium tetrachloroplatinate (1.2 g, 2.9 mmol) in acetic acid (100 mL) were added into a 250 mL flask, which gave a red suspension. The suspension was purged with nitrogen. The reaction mixture was stirred at reflux for 48 h, at which point it was cooled to room temperature and 100 mL of water were added. The product was filtered and purified by column chromatography on silica with 2:1 dichloromethane:hexane to obtain 0.72 g (33%) of Compound 1′ as a yellow solid.

Example 2 Synthesis of Compound 2′

Synthesis of 3-(1-(2,6-dimethylphenyl)-1H-imidazol-4-yl)-N-phenylaniline

A 500 mL round-bottomed flask was charged with 4-(3-chlorophenyl)-1-(2,6-dimethylphenyl)-1H-imidazole (5.39 g, 19.06 tumor) and aniline (0.870 mL, 9.53 mmol) in toluene (200 mL). Sodium tert-butoxide (4.03 g, 41.9 mmol) and dicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine (0.783 g, 1.90 mmol) were added, and the reaction mixture was degassed with nitrogen before Pd₂(dba)₃ (0.436 g, 0.477 mmol) was added. The reaction flask was evacuated and backfilled with nitrogen, and then stirred at reflux for 24 h. The crude mixture was filtered through celite, and the filtrate was concentrated in vacuo and purified using column chromatography with 10% ethyl acetate in dichloromethane to afford 1.4 g (42%) of 3-(1-(2,6-dimethylphenyl)-1H-imidazol-4-yl)-N-phenylaniline as a solid.

Synthesis of 1-(3-bromophenyl)-1H-pyrazole

1-bromo-3-iodobenzene (18.20 g, 64.3 mmol), 1H-pyrazole (4.38 g, 64.3 mmol), and (1S,2S)-cyclohexane-1,2-diamine (1.5 g, 12.9 mmol) in dioxane (400 mL) were placed into a 1 L round-bottomed flask. Copper(I) iodide 2.0 (0.613 g, 3.22 mmol) and potassium carbonate (17.78 g, 129 mmol) were added, and the reaction mixture was stirred at reflux for 19 h. The crude mixture was then filtered through a pad of celite. The filtrate was diluted with 400 mL of dichloromethane, and was washed with water. The organic layer was concentrated and chromatographed on silica gel with 5% ethyl acetate in hexane to give 7.3 g (51%) of 1-(3-bromophenyl)-1H-pyrazole as a white solid.

Synthesis of N-(3-(1H-pyrazol-1-yl)phenyl)-3-(1-(2,6-dimethylphenyl)-1H-imidazol-4-yl)-N-phenylaniline

A 250 mL round-bottomed flask was charged with 3-(1-(2,6-dimethylphenyl)-1H-imidazol-4-yl)-N-phenylaniline (1.35 g, 3.98 mmol), 1-(3-bromophenyl)-1H-pyrazole (0.89 g, 3.98 mmol), and sodium tert-butoxide (0.459 g, 4.77 mmol) in toluene (80 mL). Pd₂(dba)₃ (0.091 g, 0.099 mmol) and dicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine (0.163 g, 0.398 mmol) were added. The reaction flask was evacuated and backfilled with nitrogen twice. The reaction was stirred at reflux for 18 h, after which time the crude mixture was concentrated and purified using column chromatography, including elution with dichloromethane-hexane 1:1 followed by neat dichloromethane and finally a gradient of 1-5% ethyl acetate in dichloromethane. This gave 1.18 g (62%) of N-(3-(1H-pyrazol-1-yl)phenyl)-3-(1-(2,6-dimethylphenyl)-1H-imidazol-4-yl)-N-phenylaniline as a pale yellow foam.

Synthesis of Compound 2′

N-(3-(1H-pyrazol-1-yl)phenyl)-3-(1-(2,6-dimethylphenyl)-1H-imidazol-4-yl)-N-phenylaniline (1.2 g, 2.5 mmol) and potassium tetrachloroplatinate (1.0 g, 2.5 mmol) were added to acetic acid (100 mL) and the mixture was degassed thoroughly with nitrogen before being heated to 130° C. (bath temperature) for 14 h. The reaction was cooled to room temperature, and 100 mL of water was added. After stirring for 20 minutes, the reaction mixture was filtered through a small bed of celite and washed with copious water and then MeOH. After drying, the solid was washed off the celite with DCM. The resulting filtrate was rotovapped to give 1.4 g of a yellow solid. The crude material was chromatographed on silica gel with 9:1 DCM:hexane to give 0.94 g of Compound 2′ as a yellow solid (HPLC purity: 97.7%). The product was confirmed by NMR and LC/MS.

It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. The present invention as claimed may therefore include variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. It is understood that various theories as to why the invention works are not intended to be limiting. 

1. A compound having the formula:

wherein G has the structure:

and wherein G is fused to any two adjacent carbon atoms on ring A; wherein ring B, ring C, and ring D are 5- or 6-membered carbocyclic or heterocyclic aromatic rings; wherein L₁, L₂, and L₃ are independently selected from the group consisting of a single bond, BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′; wherein at least one of L₁, L₂, and L₃ is not a single bond; wherein X is selected from the group consisting of BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′; wherein Z₁, Z₂, Z₃, and Z₄ are nitrogen or carbon atoms; wherein A₁, A₂, A₃, A₄, A₅, A₆, A₇, and A₈ comprise carbon or nitrogen; wherein R₁, R₂, R₃, and R₄ independently represent mono-, di-, tri-, or tetra-substitution; wherein R₁ is optionally fused, R₂ is optionally fused to ring B, R₃ is optionally fused to ring C, and R₄ is optionally fused to ring D; wherein R₃ and R₄ are optionally linked to form a ring; wherein if L₂ is not a single bond, R₃ and L₂ or R₄ and L₂ are optionally linked to form a ring; and wherein R, R′, R₁, R₂, R₃, and R₄ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.
 2. The compound of claim 1, wherein the compound has a neutral charge.
 3. The compound of claim 1, wherein at least two of Z₁, Z₂, Z₃, and Z₄ are nitrogen atoms.
 4. The compound of claim 1, wherein at least two of Z₁, Z₂, Z₃, and Z₄ are carbon atoms.
 5. The compound of claim 1, wherein at least one of ring B, ring C, and ring D comprises a carbene ligand coordinated to Pt.
 6. The compound of claim 1, wherein at least one of Z₁, A₁, A₂, A₃, A₄, A₅, A₆, A₇, and A₈ is a nitrogen atom.
 7. The compound of claim 1, having the formula:


8. The compound of claim 7, having the formula:


9. The compound of claim 1, having the formula:

wherein Y is selected from the group consisting of BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′.
 10. The compound of claim 8, having the formula:


11. The compound of claim 1, wherein L₁ and L₂ are single bonds.
 12. The compound of claim 1, wherein L₃ is independently selected from the group consisting of O, S, and NR.
 13. The compound of claim 12, wherein L₃ is NR, and R is phenyl or substituted phenyl.
 14. The compound of claim 12, wherein L₃ is O.
 15. The compound of claim 1, wherein Z₂ and Z₃ are nitrogen atoms.
 16. The compound of claim 1, wherein Z₂ and Z₄ are nitrogen atoms.
 17. The compound of claim 8, wherein X is independently selected from the group consisting of O, S, and NR.
 18. The compound of claim 17, wherein X is O.
 19. The compound of claim 1, wherein the compound is selected from the group consisting of:

wherein Y is selected from the group consisting of BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′; wherein A₁′, A₂′, A₃′, A₄′, A₅′, A₆′, A₇′, and A₈′ comprise carbon or nitrogen; wherein at most one of A₁, A₂, A₃, A₄ is nitrogen; wherein at most one of A₅, A₆, A₇, A₈ is nitrogen, and the nitrogen is not bound to Pt; wherein at most one of A₁′, A₂′, A₃′, A₄′ is nitrogen; wherein at most one of A₅′, A₆′, A₇′, A₈′ is nitrogen, and the nitrogen is not bound to Pt; wherein the Pt forms at least two Pt—C bonds; wherein R₃ and R₄ may be fused together to form a ring; wherein R₅ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.
 20. A first device comprising a first organic light emitting device, further comprising: an anode; a cathode; and an organic layer, disposed between the anode and the cathode, comprising a compound having the formula:

wherein G has the structure:

and wherein G is fused to any two adjacent carbon atoms on ring A; wherein ring B, ring C, and ring D are 5- or 6-membered carbocyclic or heterocyclic aromatic rings; wherein L₁, L₂, and L₃ are independently selected from the group consisting of a single bond, BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′; wherein at least one of L₁, L₂, and L₃ is not a single bond; wherein X is selected from the group consisting of BR, NR, PR, O, S, Se, C═O, S═O, SO₂, CRR′, SiRR′, and GeRR′; wherein Z₁, Z₂, Z₃, and Z₄ are nitrogen or carbon atoms; wherein. A₁, A₂, A₃, A₄, A₅, A₆, A₇, and A₈ comprise carbon or nitrogen; wherein R₁, R₂, R₃, and R₄ independently represent mono-, di-, tri-, or tetra-substitution; wherein R₁ is optionally fused, R₂ is optionally fused to ring B, R₃ is optionally fused to ring C, and R₄ is optionally fused to ring D; and wherein R, R′, R₁, R₂, R₃, and R₄ are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. 21-59. (canceled) 